Modern phased array radars typically use thousands of radiating elements. Behind these radiators are other microwave circuitry such as amplifiers, phase shifters, attenuators, low noise amplifiers (LNAs), RF switches, etc. The current trend is to integrate a number of these functions together into a common enclosure containing both transmit and receive circuitry. This technique allows for more accurate control of the amplitude and phase of the transmitted and received signal.
Various types of adjustable attenuators exist including microwave integrated circuit (MIC) types and monolithic microwave integrated circuit (MIMIC) types. These attenuators are either voltage or current controlled, and require some sort of bias control circuitry to obtain a desired attenuation level. These current or voltage controlled adjustable-type attenuators produce a variable insertion phase that varies with attenuation level due to the varying reactive effects of the control transistors or diodes used within the attenuator devices. This insertion phase is usually quite large and can be undesirable depending upon the application. In phased array radars, this effect can greatly degrade the performance of the antenna.